This application relates to under-water appendages for water-borne sailing vessels with heavy ballast bulbs as required for International Americas Cup Class (IACC) Yachts and in particular to rotatable fin keels which produce an asymmetric effect when tacking for generating enhanced hydrodynamic forces to increase the Velocity Made Good (VMG) of the sailing vessel so as to quicken its passage to a windward destination.
In the description, the following terms have the following meanings: a xe2x80x9ccanoe bodyxe2x80x9d is the hull of the vessel up to the sheer line excluding appendages; an xe2x80x9cappendagexe2x80x9d means an underwater protrusion from the underside of the canoe body such as a keel, fin, wing, dagger board, centerboard keel, rudder, etc.; xe2x80x9cVMGxe2x80x9d (Velocity Made Good) means the velocity of a tacking or reaching sailing vessel towards its windward destination; xe2x80x9cleeward driftxe2x80x9d means the drift to leeward of a tacking or reaching vessel caused by the wind; xe2x80x9cappendage liftxe2x80x9d means a force generated by a submerged moving appendage in the direction to counter the leeward drift by the wind of a tacking or reaching sailing vessel; xe2x80x9cdragxe2x80x9d means the resistance of water passing over any submerged surface; xe2x80x9cappendage or keel dragxe2x80x9d means the resistance of water passing over wetted surfaces of a keel or an appendage; xe2x80x9cwater trackxe2x80x9d is the direction of the body of water moving towards and impinging upon a canoe body; xe2x80x9ccrabwise motionxe2x80x9d of a canoe body means that it is moving into the water track with its longitudinal axis at an angle thereto; xe2x80x9ccrabwise hull dragxe2x80x9d means the additional drag of the canoe body when it has crabwise motion; xe2x80x9cmaking leewayxe2x80x9d means that the keel or appendage is producing an asymmetrical effect to generate a hydrodynamic force vector having a component to counter the leeward drift; xe2x80x9cangle of incidence or xe2x80x9cleeway anglexe2x80x9d means the angle between the longitudinal centerline of a fin or appendage and the water track; an xe2x80x9casymmetric effectxe2x80x9d means the creation of a hydrodynamic force when the water track is split into two paths which are reunited, one path of the water flow being longer than the other path of the water flow; a xe2x80x9csymmetrical appendagexe2x80x9d means an appendage having two opposite chord surfaces each with the same camber; an xe2x80x9casymmetrical appendagexe2x80x9d means an appendage having two opposite chord surfaces of different cambers; xe2x80x9cfavorable wind shiftxe2x80x9d occurs when the apparent wind angle increases; and xe2x80x9cLift/Drag Ratioxe2x80x9d of an means its the quantity of lift per unit of drag produced by a moving submerged appendage, the goal being to generate maximum lift with minimum drag.
Velocity Made Good (VMG) of a tacking or reaching vessel is the component of the sailing yacht""s forward velocity vector which is directed towards the windward mark.
Skippers of racing yachts desire to win races and Skippers of cruising sailboats desire to shorten the time on tacking and reaching passages. Such goals can be favorably influenced with appendage design.
In exemplary embodiments of the invention, an appendage unit includes one or more thin fins carrying a heavy ballast which is supported in a manner to permit rotation of the fin(s) and the heavy ballast about an axis perpendicular to the canoe body""s waterline plane. The rotatable appendage unit is strongly fitted to its hull so as to avoid fin(s) breakage failure by bending moments thereon in heavy seas. The fin or fins are symmetrical in shape for generating a hydrodynamic force vector by water passing there over when the fin(s) are positioned at a selective leeway angle to the on-rushing water track.
In other exemplary embodiments, an articulated appendage unit has two components, one of which is rotatable to form either a symmetrical or asymmetrical appendage of selected shape, and one of which supports a heavy ballast bulb.
In exemplary methods of the invention to increase the forward velocity of a tacking sailing vessel, steps include eliminating the extra drag of a tacking canoe body which occurs when it is not arrowing into the water track and when the rotatable keel and ballast member are making leeway for increasing the canoe body forward velocity by reducing the leeward drift.
In another exemplary method of the invention to increase the forward velocity of a tacking sailing vessel, steps include tacking into the water track with a fin keel and ballast at a selected angle of incidence thereto, rotating the canoe body directly into the water track while maintaining the fin keel and ballast at the same selected angle of incidence relative to the water track and selectively adjusting the sails to take advantage of the more favorable angle of the apparent wind to the sails when the canoe body is rotated away from the apparent wind.